Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Coating device for coating powder
The invention relates to a coating device for coating powder as described
in the preamble to claim 1.
A coating device of this kind is known as a commercial product. In it, the
powder coating is applied to the workpiece by a discharge device, e.g. an
atomizer nozzle which may rotate if required, which .is fastened in place on
a robot. The coating powder is fed to the atomizer nozzle from a coating
reservoir by means of a conveyer device. 'This coating reservoir is
generally a fairly large tank which stands in a room separate from the
coating chamber.
The distance which the coating powder has to cover from the coating
reservoir to the discharge device is therefore a long one. This has the
disadvantage that the regulation of the quantity discharged is relatively
slow and the powder is therefore not applied with the optimum evenness.
Also, the coating process has to be interrupted whenever the coating
reservoir is empty and needs to be filled up again.
The object of the present invention is therefore to refine a coating device
of the kind specified at the beginning so that its reliability is increased
and its regulatability improved and it is possible for the system to be
operated continuously.
This object is achieved by the coating device specified in claim 1.
The intermediate reservoir according to the invention solves a number of
problems at the same time. Firstly, it is possible to store such a large
quantity of coating powder in it that the coating device can continue to
operate even when the coating reservoir is empty and needs to be filled up
again. In this way it is ensured that the coating device can operate
continuously.
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Because the intermediate reser~aoir has a conveyor device of its own which
feeds the coating powder to the discharge device and the coating reservoir
has a conveyor device of its own which only has to feed the coating powder
as far as the intermediate reservoir, the distance which the particular
conveyor device has to cover is shorter and the pressure drops are
therefore smaller and the regu:Latability of the quantity discharged
improved in the coating device according to the invention. Hence it is
possible to achieve a resulting coating which, overall, is more even and
more optimum.
Finally, the ratio between the installed maximum conveying capacities of
the coating reservoir conveyor device on the one hand and the discharge
device on the other ensures that there is always enough coating powder in
the intermediate reservoir (what is meant by the maximum installed
conveying capacity is the maximum conveying capacity which the particular
component is capable of achievwng. In operation, the actual conveying
capacity may be less than this;.
Advantageous refinements of the invention are specified in the subclaims.
In the event of the coating reservoir conveyor device feeding more coating
powder into the intermediate reservoir than the discharge device actually
"calls up" from it, the refinement detailed in claim 2 prevents the
intermediate reservoir from overflowing.
With the refinement detailed in claim 3, this can be done by having a level
sensor co-operate with the coating reservoir conveyor device. In the event
of the sensor being of electronic design for example, it can transmit a
signal to a control system which so regulates the conveying capacity of the
coating reservoir conveyor system or which, when required, so reduces it,
that a maximum permitted level is not exceeded in the=_ intermediate
reservoir.
A simple way of limiting the maximum level of coating powder in the
intermediate reservoir is stated in the refinement detailed in claim 4. In
the coating device specified there, excess coating powder is simply fed
back from the intermediate reservoir to the coating reservoir. Hence it is
even possible in his case for the coating reservoir conveyor device to be
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constantly operated at its maximum conveying capacity without any fear of
the intermediate reservoir overflowing.
In the refinement detailed in claim 5, the return line is positioned on the
intermediate reservoir at a height such that excess coating powder can be
fed back from the intermediate reservoir to the coating reservoir through
the return line on the "overflow" principle.
The refinement of the inventlOTl detailed in claim 6 prevents powder from
caking in the intermediate reservoir. Due to the gas-permeable fluidising
floor the coating powder in the powder compartment is kept in a fluidised
state and constantly swirled together.
If the coating device is arranged on a robot which has a fixed and a moving
section, as is usual in automobile manufacture for example, then, in
accordance with claim 7, the fixed section of the robot suggests itself as
an advantageous location for the intermediate reservoir, since the distance
from there to the discharge device arranged on the moving section of the
robot is only relatively short.
The refinement of the invention detailed in claim 8 provides a particularly
simple and safe means of transporting the coating powder from the coating
reservoir to the intermediate reservoir and from there to the discharge
device. What is meant by the term "fluidising" the coating powder in this
case is that the coating powder- is held in a suspended state in a volume of
gas and is transported with the gas as it flows.
The invention will be explained in detail by reference to the drawings, in
which:
Fig.l is a partly schematic representation of a coating device and
Fig.2 is a detail view of the intermediate reservoir of the coating device
shown in Fig. 1.
In Fig.l a coating device for coating powder is referred to generally by
reference numeral 10. It comprises a discharge device. in the form of an
atomizer nozzle 12 and which is directed at a workpiece 14 shown
schematically in the figure as a vehicle body. The coating device 10 also
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comprises a robot 16, a coating reservoir 18 and an intermediate reservoir
20. The coating reservoir 18 is situated in a remotely positioned room (not
shown), whereas the intermediat=a reservoir 20 is positioned in a coating
chamber (not shown either) which is itself in the immediately vicinity of
the robot 16. Finally, also present are a coating reservoir conveyor device
22, an intermediate reservoir conveyor device 24 and a return conveyor
device 26.
The robot 16 comprises a fixed section 28 which is connected to the floor
30 of the coating chamber. Fixed in place in the top part of the fixed
section 28 is a pivoting arm 3:?.The axis of pivot of pivoting arm 32 lies
perpendicular to the plane of t;he figure. Fastened to the end of the
pivoting arm 32 remote from the fixed section 28 is a spray arm 34 which
can pivot relative to pivoting arm 32 on an axis which lies perpendicular
to the plane of Fig.l. The atomizer nozzle 12 is fastened to the end of
spray arm 34 remote from pivoting arm 32 at a downward-pointing angle of
approximately 45°. The atomizer nozzle 12 can be pivoted, relative to
spray
arm 34, out of the plane of the figure about an axis 36. Robot 16 and the
positioning motors for pivoting arm 32, spray arm 34 and atomizer nozzle 12
are connected to a control system which is not shown.
The conveyor devices 22, 24 and 26 are conveyor devices operated by
compressed air, which are supplied from a compressed-air reservoir 38.
Coating reservoir conveyor device 22 comprises a metering-air line 40 and a
conveying-air line 42, both of which are connected on the one hand to a
connecting fitting 43 on top of coating reservoir 18 and on the other via
regulating valves 44 and 46 operated by the control system (not shown) to
the compressed-air reservoir 38. Coating reservoir conveyor device 22
further comprises a coating powder flow line 48 which runs from the
connecting fitting 43 on top of: coating reservoir 18 to intermediate
reservoir 20. The principle of conveying powder by means of metering air
and conveying air is known in the prior art and will therefore not be
described in detail below.
Intermediate reservoir conveyor device 24 likewise comprises a metering-air
line 50 and a conveying-air lire 52, which lines are connected on the one
hand to a connection 54 on top of intermediate reservoir 20 (see Fig.2) and
on the other via regulating valves 56 and 58 operated by the control system
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to the compressed-air reservoir 38. From connection 54 a powder ejection
line 60 runs to atomizer nozzle 12.
Return conveyor device 26 likewise comprises a metering-air line 62 and a
conveying-air line 64, which a~-e connected on the one hand to a connection
66 on intermediate reservoir 20 and on the other via regulating valves 68
and 70 operated by the control system to the compressed-air reservoir 38.
From connection 66 a coating powder return line 72 runs back to coating
reservoir 18. Together with connection 66 and the coating powder return
line 72, return conveyor device 26 and its components form a limiting
device 73, as will be explained in greater detail below.
Compressed-air reservoir 38 is connected to the bottom of intermediate
reservoir 20 via a regulating valve 74 operated by the control system and a
compressed-air line 76.
All the regulating valves 44, 46, 56, 58, 68, 70 and 74 are connected via
control lines (not shown) to the control system (not shown). Lines 40, 42,
48, 50, 52, 60, 62, 64, 72 and 76 may be rigid ducts or flexible hoses.
Reference will now be made to the intermediate reservoir 20 which is shown
in detail in Fig.2. This reservoir is a cylinder 78 which stands upright
and whose bottom end-face 80 is fastened to the top 82 of the fixed section
28 of robot 16.
Arranged in the interior of cylinder 78, spaced away from the bottom end-
face 80, is a disc-shaped gas-permeable fluidising floor 84 whose outer
circumferential surface (no reference numeral) co-operates with the inner
wall of cylinder 78 to form a seal. The fluidising f:Loor 84 may be a fine-
mesh metal mesh or a gas-permeable ceramic or the like. The fluidising
floor 84 can be rigidly fixed to the wall of cylinder 78 or can be mounted
to slide relative to it. The fluidising floor 84 divides the interior of
cylinder 78 into a pressure compartment 86 situated below fluidising floor
84 and a powder compartment 88 situated above fluidising floor 84. Situated
in the bottom end-face 80 of cylinder 78 is an inlet 90 into which the
compressed-air line 76 opens.
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Present in fig. 2 in the upper left region of the circumferential surface
of cylinder 78 is an inlet 92 into which the coating powder flow line 48
opens.
Connection 54 is fastened to the top end-face 94 of cylinder 78. From it a
suction tube 96 extends downwards in the longitudinal direction of cylinder
78 to a point close to the fluw~dising floor 84. Positioned on the side of
the circumferential surface of cylinder 78 opposite from inlet 92 is
connection 66. The vertical position of the latter is between that of inlet
92 and the top end-face 94 of cylinder 78. Connection 66 also communicates
with the interior of cylinder '~8.
Coating device 10 is operated as follows:
Coating reservoir 18 is first tilled with coating powder. The control
system then operates valves 44 and 46 in such a way that coating powder
makes its way out of coating reservoir 18, through coating powder flow line
48 and inlet 92, and into the powder compartment 88 of cylinder 78 of
intermediate reservoir 20 and t:he latter fills with coating powder. Valve
74 is opened at the same time t:o allow compressed ai:r to makes its way
through line 76 and inlet 90 arrd into the pressure compartment 86 of
cylinder 78 of intermediate reservoir 20. The compressed air passes through
the pores or openings in fluidising floor 84 and into powder compartment 88
and causes the coating powder Inot shown) in powder compartment 88 to be
kept in a fluidised state.
The control system operates regulating valves 56 and 58 in such a way that
metering air and conveying air are fed through lines 50 and 52, coating
powder is sucked in though suction tube 96 and is conveyed through powder
ejection line 60 to atomizer nozzle 12.
The positioning motors for pivoting arm 32, spray arrn 34 and atomizer
nozzle 12 are operated in such a way that the coating powder is discharged
onto workpiece 14 in the desired way.
Since the maximum installed conveying capacity of co<~ting feed conveyor
device 22 is higher than that of atomizer- nozzle 12 and since coating feed
conveyor device 22 is operated at constant maximum capacity, the level of
the coating powder in pressure compartment 86 of cylinder 78 of
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intermediate reservoir 20 continuously rises. As soon as it reaches the
level of the opening (not shown) through which connection 66 communicates
with powder compartment 88, limiting device 73 comes into play: in other
words the excess coating powder is then fed back by open regulating valves
68 and 70 through coating powder return line 72 to coating reservoir 18 on
the "overflow" principle. This ensures that intermediate reservoir 20 is
always sufficiently well filled with coating powder but at the same time
cannot "overflow"
The distance which the coating powder has to cover from intermediate
reservoir 20 along powder ejection line 60 to atomizer nozzle 12 is
appreciably shorter than in conventional coating devices, so that pressure
drops are kept to the minimum and a powder ejection line 60 of relatively
small diameter can be used without this detracting from the conveying
capacity of intermediate reservoir conveyor device 24. It also makes it
possible for hoses which are appreciably more flexible than larger diameter
lines to be used, thereby increasing the freedom of :robot 16.
Due to the relatively short powder ejection line 60, the dynamic
performance at atomizer nozzle 12 is relatively spontaneous, thus allowing
different requirements to be responded to quickly and a uniform resulting
coating to be achieved.
Once the coating powder situated in coating reservoir 18 has been used up,
the reservoir can be refilled with coating powder without the need to
interrupt the coating process. In other words, there is enough coating
powder present in powder compartment 88 of cylinder '78 to last for the
length of time needed to refill coating reservoir 18 with coating powder.
Intermediate reservoir 20 thus makes it possible for coating device 10 to
be operated continuously, this improving the economics of the system and
also the resulting coatings.
